Well, what day goes by when we don’t imagine landing our dream job or snagging that grant? How many days go by that we don’t look fondly on that time we pretended to be incredibly sick and took our best friend’s car to downtown Chicago and wrecked it? We actually “travel time” somewhat regularly without any specialized equipment and without creating any wrinkles in the fabric of time. So-called mental time travel employs several cognitive systems, regardless of whether we are going back to the future, or back to the past.
While imagining the future is an everyday experience for humans, it has so far been unclear what knowledge or representations we use to create future goals, given that one of the main aims of having goals is to do something new, something we may never have experienced. For that reason, some researchers have proposed that our knowledge and understanding of facts about the world cannot explain how we are able to perform mental time travel into either the past or the future, and that we instead rely on memories.
While most movie versions of time machines can move in both directions, it is not clear whether the episodic memory system, which is involved in retrieval of past memories, is also used when thinking about the future. The past can serve as building blocks for imagining the future, but memories of the past are more vivid and specific than constructions we build ourselves. Future thoughts also tend to be substantially more positive than thoughts about the past (the future positivity bias).
One limitation of past research on thinking about the future is that most studies have contrasted intentional, effortful thinking about the past and future, and involuntary and voluntary thinking about the past. It has not yet been shown that future thinking always uses the same machinery as remembering something. The remaining piece of the puzzle is, when something pops into your mind about the future, how much are you using what you already remember and have experienced in the world?
Other studies have contrasted both voluntary and involuntary memory retrieval and found that although they rely on similar episodic representations, the two types of memories also differ somewhat. Memories that come to mind involuntarily are often more specific and involve more emotional impact than memories retrieved in response to a voluntary effort. It is not clear whether future thinking, like memories, can be cued by external information, when tested in a controlled environment.
A recent study by researchers Cole, Staugaard and Bernsten in the Psychonomic Society journal Memory and Cognition sought to fill in the gaps. In order to understand whether thinking about the future is similar to remembering the past, Cole and colleagues employed a task by Schlagman and Kvavilashvili (also published in Memory and Cognition in 2008) that has been used to elicit involuntary memories. In this task, participants perform a visual categorization task while being presented cue phrases designed to elicit memories. When they experience involuntary thoughts about the past, they are then asked to write down.
Importantly, Cole and colleagues extended this paradigm to elicit involuntary future thoughts while measuring how long it took participants to identify that they were experiencing mental time travel, whether and how those thoughts affected them emotionally, and how important those thoughts were to them personally. The authors were also concerned with the specificity and distinctiveness of the thoughts that came to participants’ minds, as well as how often they had previously thought about that same thing.
In this modified task participants look for infrequently appearing vertical lines among horizontal lines presented on a computer screen. At the same time, they had to report whenever they experienced an involuntary thought, either about the past or future. Among the line arrays, short phrases like lucky find would appear; when they were presented among vertical lines, but not when they were presented among horizontal lines, participants were supposed to use that phrase as a cue to voluntarily imagine a future event or come up with a memory from the past. Experimenters framed any possible mind wandering as oriented either toward the past or the future, which was manipulated between subjects.
Half of the participants were told that sometimes thoughts about the future (e.g., goals and daydreams) would pop into their minds spontaneously. The other half were told that thoughts about the past might intrude. Irrespective of instructions, participants were instructed that whenever they had an involuntary thought, they were to record that thought in a booklet. When they had completed the portion of the experiment that elicited involuntary thoughts, they were asked to generate thoughts in response to cue phrases. At the end of the study, participants completed a questionnaire for every thought that they wrote down.
The results in general suggest that voluntary and involuntary future thinking are mostly similar in the types of thoughts that are elicited. Voluntary thoughts took longer to formulate than involuntary thoughts and were more specific, vivid, and personal. Future thoughts tended to be more positive, regardless of whether they had come to mind involuntarily or been thought up. At the same time, future-oriented involuntary thoughts tended to be something that the participants had thought a lot about relative to all the other conditions. Emotional involuntary thoughts tended to impact mood negatively when negative, and positively when positive, but this was not true for voluntary thoughts.
In light of these results, Cole and colleagues argued that involuntary future mental time travel and involuntary memories make use of similar cognitive architectures. Memories are thought to start from a bit of information (such as a word or idea), which leads to the retrieval of more and more information. When we retrieve representations of events or thoughts, we can then judge whether they are goals, daydreams, or more like actual memories.
What can we say about the cognitive systems involved in mental time travel? First of all, we can mostly conclude that if our time machine can take us back to the past, it can take us back to the future. Mental time travel, both to the future and the past, is one of the most powerful cognitive tools we have as humans, while also providing the fuel for an ever-growing number of movies creating paradoxes caused by real, and not mental, time travel. The structure of episodic memory in particular seems to allow for the reconstruction of past events as well as the construction of goals and thoughts about the future from both familiar and novel parts.